Song was born in Carmichael, California to a Hmong father and a Thai mother. She began her acting career at the age of six, appearing in commercials and television shows. Her first major role was in the film Like Mike, in which she played the love interest of Bow Wow. She went on to star in a number of other films and television shows, including The Suite Life of Zack & Cody, Wendy Wu: Homecoming Warrior, The Social Network, and Crazy Rich Asians.
In addition to her acting career, Song is also a singer. She released her debut album, The B Song, in 2005. She also appeared in the music video for Miley Cyrus's song "7 Things".
Song is currently in a relationship with actor Macaulay Culkin. They have one son together, born in April 2021.